Usually conventional laser printers include a developer unit, photosensitive drum, and the like. The laser printer forms an image on paper by supplying developer to the photosensitive drum for developing an electrostatic latent image formed on the surface of the photosensitive drum and by transferring the toner image onto paper.
With this type of conventional laser printer, the aforementioned developer unit, photosensitive drum, and the like are accommodated in a casing. The casing is provided with a cover for covering or exposing the interior of the casing. The user can open the cover in order to resolve paper jams, or replace the developer unit and photosensitive drum.
Normally, the casing is covered with an exterior cover formed of synthetic resin. However, the appearance of such a cover can decline relatively quickly due to dirt from hands or the like and scratches due to the opening and closing operations of the cover and like.
For this reason, exterior covers such as that disclosed in Japanese unexamined patent application publication No. HEI-9-222763 have been proposed. In this proposal, an exterior cover is detachably mounted on the body of the image-forming device, on the surface facing the user. This exterior cover has engaging parts, such as engaging holes forming the same shape in the same position on the front and rear surfaces of the exterior cover as viewed from she front when the exterior cover is inverted laterally, that is, in the right-to-left direction. This construction enables both the front and rear surfaces of the exterior cover to be used as the outer surface.
However, only the front and rear surfaces of the exterior cover described above can be used as the outer surface by flipping the cover laterally, that is, in the right-to-left direction. Hence, the conventional problem has not been solved since the exterior cover still easily becomes dirty or scratched and the exterior appearance of the cover cannot easily be maintained over a long period of time.
One type of conventional color laser printers well known in the art is a tandem type printer that includes four photosensitive drums corresponding to the colors yellow, magenta, cyan, and black. Electrostatic latent images formed on each photosensitive drum are developed in the respective color to form a color toner image on the photosensitive drum. Subsequently, each toner gage is transferred onto paper.
Of these tandem-type color laser printers, there have been proposed direct tandem printers having four image-forming units juxtaposed at intervals horizontally, each image-forming unit including a photosensitive drum and a developing unit, whereby a paper is conveyed horizontally so as to sequentially contact the photosensitive drum in each image-forming unit, and the image in each color is directly transferred onto the paper. Another proposed color laser printer is an intermediate transfer tandem printer having an intermediate transfer belt disposed horizontally and in confrontation with each image-forming unit, whereby the images of each color are temporarily transferred onto the intermediate transfer belt and all images are subsequently transferred at once from the intermediate transfer belt to the paper.
However, when four image-forming units are juxtaposed horizontally, a much larger footprint is required for the printer than a monochrome printer that has a single image-forming unit.
Full-color image-forming devices have been proposed to overcome this problem, such as that disclosed in Japanese unexamined patent application publication No. 2001-109325. This image-forming device has four independent image-forming stations PY, PM, PC, and PK, each having a photosensitive drum, a developing unit, a cleaning device, and the like. The image-forming stations are arranged vertically along an upward moving side of a vertically arranged transfer belt. Paper attracted to the transfer belt to each of the stations PY-PK, at which time the stations PY-PK sequentially superpose toner images in their respective colors on the paper to form a full-color image.
Since the image-forming stations in the image-forming device according to Japanese unexamined patent application publication No. 2001-109325 are juxtaposed vertically, the footprint of the image-forming device is less than that of a device having stations juxtaposed horizontally.